There is a need for a real-time, in-situ determination of the relative ratios between volatile (VOC) and semi-volatile (SVOC) hydrocarbons in sample fluid streams.
For example, increasingly stringent emissions regulations for diesel engines are resulting in tighter engineering targets for engine components. Exhaust gas recirculation (EGR) is a means for reducing NOX production by re-circulating a portion of exhaust gases from an engine back into the combustion chambers of the engine to reduce combustion temperatures. Such EGR streams are frequently cooled by use of a gas-to-water heat exchanger to enhance the cooling effect of the EGR gases on the overall combustion process. Historically, EGR coolers have not required high heat exchanger effectiveness. This is changing, however, because the low target temperatures for engine exit gases are being driven down even lower because of more stringent NOX emissions standards. This downward shift has resulted in similarly and related stringent requirements regarding heat exchanger effectiveness and issues with fouling of EGR coolers caused by particulate matter (PM) and (SVOC) deposition within gas flow paths.
Calibration to meet modern efficiency and emissions targets for diesel and other engines involves complex optimization of a large number of control parameters. Rapid assessments of PM emissions are already possible by, for example, the use of a tapered-element oscillating microbalance or an optical smoke meter. Relatively rapid total hydrocarbon measurements are possible by using a heated flame ionization detector (HFID). However, HFID measures all of the hydrocarbons present when in fact only a fraction of the overall hydrocarbons are culprits with regard to the fouling of EGR coolers. Historically, obtaining more information than is available with an HFID typically required speciation of the hydrocarbons using gas chromatography (GC). GC analysis provides much more information about the hydrocarbons than an HFID, but GC cannot be accomplished rapidly enough to support activities such as, for example, real-time engine calibration.
What is needed, therefore, is an apparatus and method for rapidly determining the relative ratios between VOCs and SVOCs in a sample fluid stream such as an exhaust gas mixture. More specifically, what is needed is an apparatus and method for rapidly determining the relative ratios between VOCs and SVOCs in the exhaust gas mixture of modern compression ignition and spark ignition engines.